Note: Descriptions are shown in the official language in which they were submitted.
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Circuit board support for laser cutting
Field
[0001] The invention relates to a support for laser cutting of a circuit
board.
Background
[0002] Circuit board material, such as FR4 circuit board, may be cut
by directing laser-generated optical energy onto a circuit board at a power
necessary for cutting. Laser radiation is focused onto a circuit board as a
small
point, whereby in the focal point area the circuit-board substance heats in-
tensely and detaches. Detachment may result from melting, burning, evaporat-
ing or the like. Detachment may be enhanced by pressurized air or gas, for
instance. Laser cutting allows board parts of electronic circuitry, printed or
to
be printed on a circuit board module, to be detached from a large circuit
board
and each circuit board part may be shaped to have a desired form. Each circuit
board part may comprise the same electronic circuit, or different circuit
board
parts may comprise different electronic circuits. Laser cutting provides a
clean
and precise cut on the circuit board without fouling and wearing a cutting
edge.
[0003] For cutting, the circuit board is placed on a support, which
may be product-specific for each circuit board part. As the support is shaped
according to a board part to be produced, laser radiation does not hit the sup-
port, and thus damage to the support is avoided.
[0004] Attempts have been made to avoid damages caused by la-
ser radiation to the support by employing a belt or slat-type conveyor
support,
which does not come into contact with the circuit board at the focal point of
laser radiation. It is possible to implement the solution, for instance, by
means
of three rolls such that the middle roll is on the support, and lower than the
other two rolls, whereby the roll protects the support while the roll and
support
location further off the focal point reduces the laser radiation force exerted
thereon per surface area unit.
[0005] Laser cutting of circuit boards poses problems, however. A
problem with a product-specific support solution is that each circuit board to
be
produced must have a specific support, which makes the cutting arrangement
complicated, expensive and prone to fault situations. In the belt and slat-
type
conveyor, where the support does not come into contact with the circuit board,
the problem is that roll locations must be changed along with laser radiation
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focusing, when the circuit board is being cut. In that case the circuit board
may
move and the laser radiation may hit a point other than intended. Furthermore,
because it is difficult to make the rolls very small, and they do not permit
for-
mation of a narrow slit equal to the focal point of laser radiation, the
circuit
board to be cut may bend at the cutting point and thus becomes off focus,
which distorts the cutting direction and deteriorates both the alignment and
the
cut. Thus there is a need to develop a support to be used in laser cutting.
Brief description
[0006] It is an object of the invention to provide an improved sup-
port. This is achieved by a support for carrying a circuit board.
[0007] The invention relates to a support for carrying a circuit board
during cutting performed by laser radiation. The support comprises a ceramic
supporting surface, on which the circuit board may be placed for cutting to be
performed by laser-generated optical radiation, the ceramic supporting surface
being configured to remain unchanged as said laser radiation hits it.
[0008] The invention also relates to a method for supporting a cir-
cuit board during cutting performed by laser radiation. In the method the
circuit
board is supported by a ceramic supporting surface of the support and optical
radiation from the laser which cuts the circuit board is received on the
ceramic
supporting surface of the support without non-reversible changes in the sup-
porting surface.
[0009] Preferred embodiments of the invention are disclosed in the
dependent claims.
[0010] The method and performance measurement system of the
invention provide several advantages. The support is not product-specific and
it withstands laser cutting.
List of figures
[0011] The invention will now be described in greater detail in con-
nection with preferred embodiments, with reference to the accompanying
drawings, in which:
Figure 1 shows cutting of a circuit board by laser,
Figure 2 shows a support comprising a plurality of support parts,
Figure 3 shows support parts with pivot-type interconnection,
Figure 4 is an example of a conveyor,
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Figure 5A shows a circuit board on the support,
Figure 58 shows a situation, in which the circuit board with its sup-
port is lifted at the cutting height, where laser radiation may cut the
circuit
board,
Figure 5C shows a situation, in which the cut circuit boards are low-
ered on the support from the cutting height, and
Figure 6 is a flow chart of the method.
Description of embodiments
[0012] Figure 1 shows how a circuit board is cut by means of laser
radiation. The circuit board 106 may comprise components 112 or the circuit
board 106 may be without components. The components 106 may be electron-
ic, optical, optoelectronic, mechanical or the like, without being restricted
there-
to, however. The circuit board 106 may comprise an FR4 laminate or other
circuit board material used in electronic circuit manufacture. Thus, the
circuit
board 106 may also be flexible, such as FPC (Flexible Printed Circuit).
[0013] A support 100, which is at least approximately horizontal
such that the circuit board 106 will stay in place without sliding on the
support
100 by means of friction, may be completely ceramic, in which case it has a
ceramic supporting surface 102 against the circuit board 106 to be placed on
the support 100, or it may comprise a separate ceramic supporting surface
102, on which the circuit board 106 may be placed. In that case the other ma-
terial 104 in the support 100 below the ceramic supporting surface 102 may be
metal. Metal enhances impact resistance of the support 100, for instance. In-
stead of metal, the other material 104 may also be plastic. In addition, the
oth-
er material 104 may be a combination of various materials.
[0014] The supporting surface 102 of the support 100 is ceramic so
that the circuit board 106 could be safely cut by means of the optical
radiation
110 generated by the laser 108. The laser 108 may be a carbon dioxide laser
(CO2 laser), a neodymium laser (Nd laser), a neodymium-doped yttrium alu-
minium garnet laser (Nd YAG laser) or the like. In principle, optical
radiation
110 the laser 108 emits may be ultraviolet light, visible light or infrared
light. In
many cases, the radiation emitted by the laser 108 is infrared and within the
range of 1pm to 20pm, for instance. The carbon dioxide laser, for instance,
may operate at the wavelength of about 10pm. The optical radiation 110 of the
laser 108 may be focused onto the circuit board 106 as a focal point whose
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diameter may be just tenths or hundredths of millimetres, without limiting
there-
to, however.
[0015] The optical radiation generated by the laser 108 cuts a hole
in the circuit board 106 and as the focal point of the optical radiation 110
is
moved in relation to the circuit board 106, circuit board parts of desired
shape
may be cut off the circuit board 106. The ceramic supporting surface 102 re-
mains unchanged, however, even though the laser radiation 110 hits it. So, the
ceramic supporting surface 102 withstands possible focussing of energy origi-
nating from the laser radiation 110 and a resulting rise in temperature
without
breaking and deforming permanently. For instance, a minor change caused by
thermal expansion is fully reversible. The material of the supporting surface
102 withstanding optical radiation of the laser 108 may be porcelain, for in-
stance. Alternatively or additionally, the supporting surface 102 may be of
herlite and/or burnt clay.
[0016] From the supporting surface 102 optical radiation generated
by the laser 108 may reflect and/or scatter towards the circuit board 106. The
supporting surface 102 may, however, damp the reflected/scattered laser radi-
ation 110 so much that the optical radiation from the support to the circuit
board 106 will not alter or damage the circuit board 106. The damping is
based, for instance, on the roughness of the supporting surface 102, which
affects the scattering, and on the reflection coefficient, which affects the
inten-
sity of reflection, on the wavelength range used by the laser 108.
Sufficiently
high scattering and/or reflection dampening are thus useful.
[0017] In some cases a randomly selected, ceramic supporting sur-
face material is sufficiently good. Sometimes the supporting surface material
is
to be optimised according to the optical radiation power used in cutting and
the
strength of the circuit board material to be cut. The supporting surface 102
may thus be strongly scattering at the wavelength of the laser, which is
provid-
ed by unevenness exceeding the wavelength in the surface. Average rough-
ness may thus be inferior to the size (e.g. diameter) of the focal point in
the
optical radiation 110 of the laser 108. Further, average roughness of the sup-
porting surface may be superior to the wavelength in the optical radiation 110
of the laser 108. Thus, the average roughness in the supporting surface 102
may range from ten micrometres up to millimetres, if the laser wavelength is
about 10 micrometres. In addition, the supporting surface 102 may reflect
poorly the optical radiation 110 of the laser 108. In that case, the
supporting
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surface 102 may reflect only less than half of the optical radiation 110 of
the
laser 108 directed thereto, for instance. With appropriate choices of material
the supporting surface 102 may also be rendered so poorly reflective that the
reflection is just from a few per mille to a few tens of per cent of the
optical ra-
diation 110 of the laser 108 directed to the supporting surface 102.
[0018] Figure 2 shows an embodiment in which the support 100
comprises a plurality of support parts 120 to 126 which may be separate or
interconnected. Each support part 120 to 126 comprises, however, a ceramic
supporting surface 102. The support 100 may be e.g. a slat-type conveyor,
whose slats may be connected to a movable chain 250. The slat-type convey-
or permits a horizontal turn of desired degree and thus the support 100 of the
slat-type conveyor may also rotate in a horizontal circle. The slat-type
convey-
or may be intended to transfer circuit boards 106 for being cut with the laser
108. On the circuit boards 106 the components may be in place, and conse-
quently the circuit board 106 may be ready for service.
[0019] Figure 3 shows a support consisting of support parts 120 to
126. The support parts 120 to 126 of the support 100 may be interconnected
with pivots 300.
[0020] Figure 4 shows a conveyor whose part serving as the sup-
port 100 is circular in vertical direction. The support 100 may rotate
endlessly
between end rolls 400, 404 and move circuit boards 106 supplied to the sup-
port 100 for being cut by the optical radiation 110 of the laser 108. There
may
be more than two rolls 400, 402, 404, whereby the support 100 may also be
carried between the end rolls 400, 404. Also in this case the conveyor support
100 comprises a ceramic supporting surface 102, which comes into contact
with the circuit board 106. Further, the support 100 may comprise support
parts 120 to 126, which may be pivotedly interconnected, as shown in Figure
3, in order to enable the support 100 to curve along with the surface of the
rolls
400, 404. After the cut performed by the laser 108, the circuit board parts
406,
408 cut off the circuit board 100 may be transferred from the support 100 to a
desired place or for further processing.
[0021] Figure 5A shows a circuit board 106 which lies on a support
100 and where circuit board parts to be cut 406, 408 are marked. An edge por-
tion not belonging to the circuit board parts 406, 408 of the circuit board
100 is
indicated by reference numeral 500.
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[0022] Figures 5B and 5C show the principle how the circuit board
parts 406, 408 are separated from the rest of the circuit board after cutting.
Figure 5B shows an embodiment, in which each support part 120 to 126, such
as a slat, may be detached and lifted for the cutting process. This conveyor
may be a pallet conveyor, for instance, and the lifting may be performed by
means of pressurized air generated by a pneumatic cylinder. Instead of the
pneumatic cylinder, it is also possible to use other lifting mechanisms. After
lifting, when the circuit board 106 is up, the circuit board 106 may be set
accu-
rately onto a predetermined place with holders 502 for being cut. Thee holders
502 may, for instance, press the circuit board 106 such that the circuit board
106 remains in place. How the circuit board 106 will be held in place during
cutting (or whether it will be held at all) is not relevant to this
application.
[0023] Figure 5C shows a situation, in which the support part 120
(or any one of the support parts 122 to 126) is lowered back to the level of
oth-
er support parts. In that case the circuit board parts 406, 408 have come down
together with the support part 120, but the edge portion 500 of the circuit
board
106 is still up in the holder 502. The edge portion 500 may be shifted from
the
holder 502 for disposal or recycling. After cutting, the support part 120
moves
onwards so that a next circuit board 106 on a next at least one support part
122 to 126 can be cut.
[0024] Figure 6 is a flow chart of the method. In step 600, the circuit
board 102 is carried on a ceramic supporting part 102 of the support 100. In
step 602, optical radiation 110 of the laser 108 cutting the circuit board 102
is
received on the ceramic supporting surface 102 of the support 100 without
non-reversible changes in the supporting surface 102.
[0025] Even though the invention is described above with reference
to the attached drawings, it is clear that the invention is not restricted
thereto,
but it may be modified in a variety of ways within the scope of the accompany-
ing claims.
